The field of this invention is fiber optic switching systems.
Fiber optic switching systems have been developed and used successfully in industrial applications. Such switching systems typically include a fiber optic transmitter, a fiber optic switch, a fiber optic receiver, and fiber optic cable connecting the components. The transmitter and receiver are usually located on an input/output card, such as might be used in an industrial controller, and the fiber optic switch is remotely located.
In prior switches, an opaque shutter is used in the switch mechanism. The shutter can be inserted into the optical path to block the passage of light from the transmitter to the receiver or withdrawn from the optical path to allow the light's passage. The receiver detects the presence or absence of light in the switch output and thus determines the state of the switch.
In prior fiber optic switching systems, the receiver interprets a fault condition such as a break in the fiber optic cable the same as a closed switch. That is, the receiver detects the absence of light when either the switch is closed or if the fiber optic link is faulty, regardless of the state of the switch. Therefore, a need exists for a fiber optic switching system which discriminates between a fault condition and normal system operation.